Method of preparing a papermaking pulp by mercerizing and etherifying in a non-agingcondition



Sept. 5, 1967 B. B. THOMAS EVAL 3,340,139

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GEORGE B. CREAME BY Wan/514] Sept. 5, 1967 B. B. THOMAS ErAL 3,340,139

A METHOD OF PREPARING A PAPERMAKING PULP BY MERCERZING AND ETHERIFYING IN A` NON-AGING CONDITION Filed April 19, 1966 5 Sheets-Sheet .5

ATTORNEYS Ow Om Sept. 5, 1967 B- B THOMAS ETA'- 3,340,139

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spuoaas aaumsgsag JW INVENTORS BERWYN B.THOMAS GEORGE B. CREAMER ATTORNEYS Sept. 5, 1967 Filed April 19, 1966 Air Resistance, seconds B. THOMAS ETAL 3,340,139

METHOD OF PREPABING A PAPEHMAKING PULP BY MERCERIZING AND ETHERIFYING IN A NON-AGING CONDITION v 5 Sheets-Sheet FIG. 9

Gurley Air Resistance versus Beating Time Series Based on Sulfiie Curves AEnd at 200 C.S.F.

Beating Time, minutes INVENTORS BERWYN B.THOMAS GEORGE B. CREAMER BY @www w/zak wml/1757@ {Qca/m4,]

ATTORNEYS United States Patent Oli-ice 3,340,139 Patented Sept. 5, 1967 3,340,139 NIETHOD OF PREPARING A PAPERMAKING PULP BY MERCERIZING AND ETHERIFY- ING IN A NON-AGING CONDITION Berwyn B. Thomas, Shelton, Wash., and' George B. Creamer, Thornwood, N .Y., assignors to Rayonier Incorporated, Shelton, Wash., a corporation of Delaware Filed Apr. 19, 1966, Ser. No. 543,705 3 Claims. (Cl. 162-72) ABSTRACT F THE DISCLOSURE In the process of this invention, a papermaking grade of wood pulp is mercerized as rapidly as possible with from 12 to 25 percent sodium hydroxide solution at from about 5 to 40 C. in the substantial absence of oxygen and the excess caustic-quickly removed. Without delay the resultant non-aged, alkali-purified, mercerized Wood pulp is quickly shredded and etherited with from 2.5 to 8.0 percent ethylene oxide or propylene oxide while still in the s-ubstantial absence of oxygen, neutralized with dilute acid and washed to provide an improved, -mercerized furnish that can be formed into a strong, porous paper with increased brightness and color stability.

This application is a continuation-impart of our application tiled Dec. 10, 1963, Ser. No. 329,384, now abancloned.

This invention relates to papermaking woodpulp and to the paper made therefrom. More particularly the invention relates to a process for preparing a mercerized woodpulp furnish so that it can be formed into an improved strong, porous paper with increased brightness and color stability.

It is well known that mercerizing sharply reduces the inherent inter-liber bonding characteristics of cellulosic fibers. This fact has heretofore prevented the use of mercerized fibers as any substantial portion `of the furnish when making strong papers since the strength of the paper is directly related to the inter-fiber bonding ability of the furnish. This has been the case even though mercerization otherwise greatly enhances the purity, brightness and color stability of both the fibers and the paper. Over the years a great deal of eff-ort has been expended seeking a pracn tical method of restoring the inter-fiber bonding characteristics to mercerized cellulosic fibers without success.

As a solution of the foregoing problem we found that when a woodpulp is .mercerized and immediately etheritled under carefully controlled non-aging (non-depolymerizing) conditions to substitute thereon from about 2.5 to 8.0 percent ethylene oxide or propylene oxide, followed by neutralizing, the result is a wood pulp having surprising properties for making paper. Further investigation then disclosed that woodpulp mercerized and etheriiied under non-aging conditions could be used as the total furnish in prepa-ring an improved strong paper with high flexibility and increased porosity and color stability.

In the preferred process of the invention a kraft or sulfite type wood pulp, suitable for the production of strong paper is first mercerized and shredded as rapidly as possible under carefully controlled non-aging and non-depolymerizing conditions and then immedi-ately etheritied and neutralized under non-oxidizing conditions. The mercerization is carried out with from about 12 to 25 percent aqueous sodium hydroxide solution at a temperature from about 5 to 40 C. the steeping is -continued only as long as necessary to obtain a uniform absorption of the caustic solution into the pulp (about 3 to 10 minutes depending upon the equipment used, the caustic concentration and the temperature). The non-aging conditions during mercerizing are achieved by coverage of the fibers with the caustic solution since the aqueous caustic phase effectively shields the lalkali cellulose from the oxygen of the air during the short time required for steeping. The steeped iber is then quickly pressed to remove the excess sodium hydroxide and rapidly shredded to a uff keeping overall contact with air at a minimum by promptly carrying out the operation in enclosed equipment from which air is displaced by an inert gas, for example nitrogen. The elapsed time for mercerizing and shredding should not exceed 45 minutes and if practical it is preferable that is not exceed 30 minutes. The foregoing treatment will minimize the adverse elfect of oxygen and aging on the cellulose and the inherent inter-fiber bonding characteristics of the mercerized fiber.

Immediately upon completion of the tluiiing of the nonaged mercerized liber, it is placed in a suitable closed container and etheriiied with sutiicient ethylene oxide or propylene oxide to substitute thereon from about 2.5 to 8.0 percent by weight. The etherication is carried out in the substantial absence `of gaseous oxygen,- preferably in nitrogen, and at approximately the same temperature range as the mercerization. Following etherication the fiber is quickly neutralized with dilute acid to avoid aging and washed. It is then ready to be made into paper by the usual methods.

In the process of the invention, avoidance of depolymerization (aging) of the cellulose by minimizing of contact of the alkaline fiber with oxygen and the strict observance of the indicated conditions for mercerization and shredding, and the introduction of a sufficient quantity of ethylene oxide or propylene oxide are all important to its success. Aging, due to oxidation, injures the iibers and renders the paper weak. Excessive etherication makes the tibers alkaliand, when carried far enough, water-soluble. Using the particular combination of treatments -and observing the conditions specified in this invention, however, the mercerized woodpulp thereafter obtained can be beaten in conventional equipment to the degree of freeness required for the desired type of paper, cast into paper on conventional equipment and dried in a conventional manner to provide a paper with exception-ally high strength, porosity, flexibility, transparency and color stability.

The following examples illustrate the invention in greater detail.

EXAMPLE I Portions of a commercial kraft wood pulp made from southern pine, having a degree of polymerization around 1300 were marked (A) to (D) for identification, and treated as follows:

(A) This portion was used as a control. It was given no treatment prior to beating and papermaking.

(B) This portion of pulp was mercerized by steeping 30 minutes in 18.5% aqueous NaOH solution at 25 C., pressed to a weight ratio of 2.5, and shredded one hour in a batch shredder. The alkali cellulose crumb was then aged 24 hours at 30 C. In the presence of a trace of manganese, neutralized and washed.

(C) This portion of the pulp was lalso mercerized by steeping 30 minutes in 18.5% aqueous NaOH solution at 28 C. and pressed to a weight ratio of 2.5. It was then shredded to a density of 0.15 by a single pass through a Sprout-Waldron continuous flutter from which oxygen was excluded by nitrogen pressure. At the end of the shredding the alkali cellulose was at once neutralized with dilute sulfuric acid yand Washed until neutral, so that degradation of the cellulose was etfectively prevented.

(D) This portion of pulp was treated by the process of the invention. It was mercerized and shredded as was Y 3 sample (C). The shredded alkali cellulose was transferred, with exclusion of air by nitrogen, to a closed continuous TABLE I reactor vessel having a jacket maintained at 73 C. Any A B C D remaining traces of oxygen were removed by evacuation and replacement with nitrogen, and pressure of nitrogen 5 Treatment: was maintained on the vessel. Ethylene oxide was ad- Mercerized. N0 Yes Yes Yes mitted by mixing it with the nitrogen at a concentration nef gg gg ,of 50 mol percent and a r-ate assuming 50 percent eici- A {Ettnoxrptercena o o 0 3,7

Ua y 102i a 8.1 ency of reaction with the cellulose. The cellulose was re- Degree epelymezaeien 1,290 640 17200 1 210 tained in the reaction chamber for 21 minutes, and had 10 grigiiessieroei ggg g1g 90.7 89.3 rig ness, ea. ge ,percen 6. 88.8 88.4 then absorbed 3.7 percent of ethylene oxide by weight. BehmesSY U V Aeempereent 7M 84.8 829 8m On leavmg the chamber the cellulose was immediately rviaiiperooiit 8.3 is 2.5 i3 neutralized with dilute sulfuric lacidwashed untilacid- Paperfllgtsbb-s'ip 6'5 26 4-0 2'6 free, and given a treatment with dilute sulfur dioxide Beating Timer/nii es 9s 9s 126 Solution 1 Burst 73 35 5l. 86 5 Toor 151 iso isa iev ln order to illustrate the effect of the foregoing treat- 1 o1 1, No 8 600 4 85 600 3,300 ments on the papermaking characteristics of the southern Olitee.: peert 5-f2 7gg efg 85(2)?? pine kraft pulp, the products (A) and (D) were each Alf Rslstance, Sec 35 10 25 23 Slllrried in Water and beaten in a Valley beater by a Strate pement 25 4'0 42 6'4 method closely similar to that of TAAPI Method T 200 ts-61. Progress of the beating was followed by tests for EXAMPLE II Canadian Standard Freeness, by TAPlPI Method T 227 rrr-58. Freeness of the pulp was reduced from an initial Further portions of the commercial bleached southern value near 750 to below 200 where beating was stopped. P Hle kfaf'f-PU1P l5ed 111 'EXamPle I Were faken fOr addl- Samples of the beaten pulps taken from the beater at tional testing to illustrate the effects of process variables intervals of 15 minutes were made into handsheets and 011 quality 0f the Paperdiied by TAPPI Method T 20s iii-ss. The handsheets (E) Thls portion 0f the pulp was treated 11k@ sample TABLE II D E F G H Anal tical Data:

Bythoxyl, percent 4- 0 4 0 3.0 2. 2 5. 9 Conc. Mercerzing Caustic, percent.- 18. 5 14 22 18. 5 18. 5 Degree of Polymerization 1, 210 1, 040 1 075 970 930 Brightness, percent 89. 3 88. 5 89.1 Brightness, Heat Aged, percent 88.4 87. 7 Brightness, U.V. Aged, percent 85. 2 84. 6 Xylan, percent 1. 3 0. 9 Mannan, percent 2. 6 1. 9 Papermakiug Data (300 CSF) Beating Time, Min 126 107 Bur 86 82 Tear 167 155 Tensile, M. 8,200 8,900 Folds, No a, 300 6, 000 Opacity, percent 50.7 44.3 Air Resistance, Sec.. 23 40 Stretch, percent 6. 4 8.0

were tested by standard methods, including the following TAPPI methods:

AT 402 Am-49 (Conditioning Paper for Testing) T 403 ts-63 (Bursting Strength) T 404 os-61 (Tensile Strength) T 414 ts-64 (Internal Tearing Resistance) T 423 iii-50 (Folding Endurance) T 425 m-60 (Opacity of Paper) T 460 m-49 (Air Resistance) T 457 n1-46 (Stretch of Paper) Data obtained by these tests Iare illustrated in FIGURES 1 through 3 of the accompanying drawings. For comparison of the Various samples at an equivalent of beating their qualities at Canadian Standard Freeness of 300 were arbitrarily selected. Values abstracted from the drawings at Freeness 300 are collected in Table I.

In addition to the papermaking tests, analytical studies were made by standard laboratory methods to determine other qualities of the samples, including the :following:

(i) Brightness, on freshly made special handsheets and on the same sheets after aging in heat (16 hours at 105 C.) or ultraviolet light (3 hours) (ii) -Degree of polymerization (DP), by viscosity of solutions of the cellulose in cupriethylenediamine (iii) Xylan and mannan, by chromatography of hydrolyzates in comparison with known sugar solutions. 'Ihe results of these tests are shown in Table I.

(D) in Example I except `that the strength of the mercerizing caustic was reduced from 18.5 percent to 14.0 percent.

(F) This portion of the pulp was treated like sample (D) in Example I except that the strength of the mercerizing caustic was increased from 18.5 Apercent to 22 percent, and the hydroxyethylation was continued only until 3.0 percent ethylene oxide was added onto the cellulose.

(G) This portion of the pulp was treated like sample (D) in Example I except that hydroxyethylation was only continued till 2.2 percent ethylene oxide had been substituted on the cellulose instead of 4.0 percent.

(H) This portion of the pulp was treated like sample (D) in Example I except that hydroxyethylation was con-y EXAMPLE III The following example illustrates the use of sulte pulp and the eifectiveness of propylene oxide in the process ofthe invention:

(I) A portion of a commercial western hemlock bleached sullite pulp was used for a control sample without any treatment.

(I) A second portion of the same pulp as in the previous sample was steeped in an 18.5 percent aqueous NaOH solution at 25 C. for 5 minutes, pressed, and ued under non-aging, non-oxidizing conditions. The flued pulp was then quickly transferred to a closed reaction vessel with an agitator and hydroxyethylated in a nitrogen atmosphere with suiiicient ethylene oxide to substitute 4.1 percent on the cellulose in 35 minutes at 38 C. The product was then quickly removed from the reactor, neutralized with dilute sulfuric acid, washed acid free with water and dried.

(K) A third portion of the same pulp as used in (I) above was mercerized and etheried in exactly the same way as in the preceding sample (J) except that the etherication was with suicient propylene oxide to substitute 4.1 percent on the cellulose at 46 C. within 40 minutes.

These samples as in the preceding cases were beaten in water in a Valley beater and their papermaking qualities at a Canadian Standard Freeness of 300 determined by the same TAPPI methods.

TABLE HI Analytical Data:

FIGURES 7 to 9 of the accompanying drawings illustrate the results in Table HI.

In the foregoing Example I, the harmful eifect of mercerizing and aging on paper strength is evident from comparison of sample (A) with sample (B) (FIGURES 1 and 2). Prevention of aging alone [sample (C)] did not restore the original strength, but hydroxyethylation under non-aging conditions [sample (D)] led to formation of a strong, highly exible paper. FIGURE 3 shows that this hydroxyethylated pulp had very low air resistance (high porosity) even at a degree of beating which develops strong paper.

Other data obtained on samples (A) through (D) (Table I) show the purifying eiect of mercerzing on the fiber and the improved brightness permanence as well as good strength and very low opacity.

Example Il illustrates the etect of changes in concentration of the mercerizing caustic solution and of the degree of substitution with ethyleneoxide on the ber. The quality of the hydroxyethylated fiber was relatively independent of caustic solution concentration within the mercerizing range. It was highly dependent on the degree of substitution with ethyleneoxide, however, but while higher strengths were obtained with more ethyleneoxide the product also became more sensitive to alkali and water.

We believe the mechanism of the effect of this substitution to be approximately as follows: during mercerization the crystalline form of the cellulose is changed and many impurities are removed. This results in an open structure within the liber which shrinks sharply on neutralizing and shrinks further on drying thereby forming many relatively permanent internal bonds. There is little tendency to inter-liber bonding because the fibers are sti and have fewer surface iibrils or swollen portions than before mercerizing. A normal mercerizing procedure also permits the oxygen to attack the cellulose reducing its DP.

Substitution of ethyleneoxide on this liber, while still in an alkaline stage prevents the shrinkage on neutralization and provides new links of a more ilexible, hydrophilic type. The fiber is accordingly more plastic and its internal irregularities are lled in. This reduces interfaces which produce opacity and increases areas Where fibers touch. The increased contact and availability of surface bonding groups and prevention of degradation restore the good strength, iiexibility and porosity are derived from the open sheet structure that results from removal of small fragments and resistance of the fiber to fragmentation in beating.

Papers made with liber produced according to this invention are advantageous for use in filters, absorbent products, laminating and decorative papers, permanent record papers and parchments among others.

We claim:

1. The process of making mercerized papermaking wood pulp which comprises mercerizing the pulp libers, in the substantial absence of free oxygen, with from 12 to 25 percent sodium hydroxide solution for three to 10 minutes at from 5 to 40 C., providing an atmosphere of inert gas, rapidly removing the excess sodium hydroxide and shredding the mercerized iiber to a ilutf in said atmosphere, said steeping and shredding being completed within less than 45 minutes time and then immediately etherifying the iluied fibers, without removing them from the atmosphere of inert gas, with from 2.5 to 8.0 percent of an alkylene oxide selected from the group consisting of ethylene oxide and propylene oxide, substantially immediately neutralizing residual alkali in the etherified pulp with dilute acid to avoid substantial aging and then washing with water.

2. The process of claim 1 wherein the papermaking wood pulp is a kraft-type papermaking wood pulp and wherein the iluied ibers are etheriiied with ethylene oxide.

3. The process of claim 1 wherein the papermaking wood pulp is a bleached kraft-type papermaking wood pulp and wherein the fluied fibers are ethen'iied with from about 3 to 5% of ethylene oxide.

References Cited UNITED STATES PATENTS 2,533,145 12/1950 Schorger 162-157 3,031,371 4/1962 Beyer et al. 162-146 S. LEON BASHORE, Primary Examiner.

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No 3 ,340 ,139 September 5 1967 Berwyn B. Thomas et a1 It is hereby certified that error appears in the above numbered patent requiring correction and that the said Letters Patent should read as corrected below.

Column 2, line 12, for "is", second occurrence, read 1t line 64, for "28 C." read 25 C. column 3, line 61, after "equivalent" insert degree Signed and sealed this 27th day of August 1968 (SEAL) Attest: Edward M. Fletcher, Jr. EDWARD J. BRENNER Attesting Officer Commissioner of Patents 

1. THE PROCESS OF MAKING MERCERIZED PAPERMAKING WOOD PULP WHICH COMPRISES MERCERIZING THE PULP FIBERS, IN THE SUBSTANTIAL ABSENCE OF FREE OXYGEN, WITH FROM 12 TO 25 PERCENT SODIUM HYDROXIDE SOLUTION FOR THREE TO 10 MINUTES AT FROM 5* TO 40*C., PROVIDING AN ATMOSPHERE OF INERT GAS, RAPIDLY REMOVING THE EXCESS SODIUM HYDROXIDE AND SHEDDING THE MERCERIZED FIBER TO A FLUFF IN SAID ATMOSPHERE, SAID STEEPING AND SHREDDING BEING COMPLETED WITHIN LESS THAN 45 MINUTES TIME AND THEN IMMEDIATELY ETHERIFYING THE FLUFFED FIBERS, WITHOUT REMOVING THEM FROM THE ATMOSPHERE OF INERT GAS, WITH FROM 2.5 TO 8.0 PERCENT OF AN ALKYLENE OXIDE SELECTED FROM THE GROUP CONSISTING OF ETHYLENE OXIDE AND PROPYLENE OXIDE, SUBSTANTIALLY IMMEDIATELY NEUTRALIZING RESIDUAL ALKALI IN THE ETHERIFIED PULP WITH DILUTE ACID TO AVOID SUBSTANTIAL AGING AND THEN WASHING WITH WATER. 